Ozone gas (O3) provides a powerful disinfectant and oxidant when used for the treatment of water. Ozone is environmentally friendly, and decomposes to the more stable diatomic allotrope of oxygen (O2), during water treatment, minimising harmful bi-products.
Each three atom ozone molecule is relatively unstable and readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. Ozone provides a strong, broad spectrum disinfectant, and is an effective agent to inactivate harmful protozoa, microbes and other pathogens.
Ozone is commercially made by passing oxygen through ultraviolet light or alternatively using an electrical discharge. The most common ozone production technique involves corona discharge, whereby a high voltage electrical discharge is passed across a gap through which filtered dry air flows.
Ozone when used for water purification is generally created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-products and the absence of taste and odor problems which are prevalent in comparison when chlorination is used to treat water. Another advantage of ozone is that it leaves no residual disinfectant in the water after treatment has occurred. Ozonation can be used to treat organic and inorganic contaminants, including bacteria, viruses and protozons.
Whilst ozonation provides an effective means for water treatment in various applications from swimming pools to potable drinking water, there are inherent drawbacks in existing ozonation systems. One problem is the need to efficiently mix the ozone source with the water requiring treatment. For disinfection to occur, the ozone molecules must physically contact the contaminant to react with it. If an inadequate degree of mixing occurs, there is a risk of the ozone not coming into contact with parcels of water, and accordingly only partially treating the water.
This drawback is compounded by the short life span of the ozone molecule, which typically degrades in a short period of time back to the diatomic allotrope of oxygen (O2), after the third atom, disassociates from the ozone particle as a free radical. As such, the ozone molecules normally only last for a few minutes or less after adding to water. Accordingly, if the ozone molecules do not come into contact with the contaminants shortly after being introduced into the water flow, the likelihood of effective water treatment is significantly reduced.
In addition, on account of the added electrical input and hence costs associated with producing the ozone, it is preferable to minimise the ozone production, and not produce surplus ozone beyond what is required for adequate decontamination.
A further problem with ozone treatment is that the water will almost always need to be filtered or settled after ozone exposure, as ozone tends to coagulate and precipitate various impurities present in the water.
The size of the ozone gas bubble released into the water for treatment is an important factor. A bubble size of 2 to 3 microns is generally desirable, and for good gas to liquid transfer, the smallest achievable bubble size is generally preferable. Ozone gas is difficult to efficiently mix into an aqueous solution. In order to reach the full potential of the ozone to treat the water, saturation of the ozone gas in the aqueous solution is generally required.